Wireless sensor networks are known to be used in process control systems. Examples on such networks are ZigBee and WirelessHart, ISA100, WIA-PA and Bluetooth. There also exist some WLAN based sensor networks.
These networks often employ a time division communication scheme, such as Time Division Multiple Access (TDMA), where a wireless communication device in the form of field device may access resources in the form of time intervals of the scheme for communication with the process control system.
Some wireless networks use a fixed allocation of the time interval to field devices. This requires a network manager or radio resource manager that manages the resources.
Weights have also been used for various purposes in data networks.
US 2008/0253290 does for instance describe optimization of traffic distribution in a communication network with multipath routing. Distribution weightings are provided for a node of the communication network which has several alternatives or downward links for the routing to a target. The distribution weightings are modified relative to each other as a measure of the traffic loading on the downward links in order to reduce distributed traffic on highly loaded links and to increase distributed traffic on the less loaded links.
US 2006/0209785 describes a method of routing data packets across a multi-layer network which includes a plurality of nodes, a logical level provided with a plurality of logical links and a physical level provided with a plurality of physical links, each of the logical links corresponding to at least one of the physical links. The method comprising assigning a weight to each logical link with respect to a first critical constraint in the logical level, refining the weight assigned to each logical link with respect to a second critical constraint in the physical level and, based on the weights assigned to each link, computing a path at the logical level connecting a start node to an end node for the transport of the data packets.
US 2006/0168317 describes the routing of data packets comprising a target address in a packet switching data network. A first and second transmission path are assigned respective traffic distribution weightings in a routing table for individual target addresses that is assigned to a network node, wherein weightings indicate the respective allocated traffic load per transmission path. The maximum traffic distribution weighting is assigned to the respective first transmission path and the minimum traffic distribution weighting is assigned to the second transmission path. During undisturbed operation, data packets are routed via the first transmission path and if the path is interrupted, the packets are routed via the second transmission path.
US 2011/0164565 describes a method of routing a wireless network. The method is performed by each of a group of nodes and includes: receiving a routing request signal; determining whether a node itself is a destination node, by referring to a traffic distribution table showing traffic throughput of the group of nodes and an intermediate-node weight table showing weights of intermediate nodes on all paths between the group of nodes and a source node, wherein a route path is selected by referring to the weights of intermediate nodes; and when it is determined that the node itself is the destination node transmitting a routing response signal to the source node that has transmitted the routing request signal, and receiving a packet from the source node, wherein the transmitting and receiving are performed by the determined destination node.
Reliable and robust wireless communication between field devices in industrial networks is of highest importance in order to guarantee 24 hour operation 7 days a week. Routing algorithms are important for Industrial Wireless Sensor Networks in order to guarantee packet delivery within the deadline required by industrial applications. In TDMA-based Industrial Wireless Sensor Network, source routing and graph routing are two available routing schemes which exist today.
High reliability and low latency is crucial for industrial applications. Both source and graph routing cannot thoroughly fulfill these requirements. A source routing scheme routes packets by establishing a fixed path from the source to the destination. If any node or link through this path fails, the communication will be terminated. Graph routing schemes are more reliable than source routing by providing additional paths from the source to the destination. However, when the network topology changes, it will take a long time to generate a new graph. During the graph adjusting period, the communication in this network may also be terminated. All of this may lead to economic loss or a safety problem, which is unacceptable for industrial applications.
There is therefore a need for an improvement in relation to industrial wireless networks.